Synthesis and Characterization of Accessible Metal Surfaces in Calixarene-Bound Gold Nanoparticles

Abstract

Use of organic ligands to partially passivate nanoparticles against sintering yet retain a degree of small molecule accessibility to the metal surface has been a lofty goal in functional materials synthesis, which in principle also enables the design of preferred electronic and steric environments on a nanoparticle surface. Catalysis using gold in particular requires donor ligands that facilitate an electron-rich metal surface and generalizable strategies for dealing with deactivation due to sintering. Here, synthesis and characterization of gold nanoparticles postsynthetically modified with the chelating ligand cone-5,11,17,23,29,35-hexa(tert-butyl)-37,39,41-tris(diphenylphosphinomethoxy)-38,40,42-trimethoxycalix[6]arene (1) is reported. In solution as well as when supported on the surface of TiO2, nanoparticles modified with tripodal calix[6]arene phosphine ligand 1 demonstrate enhanced protection against sintering relative to unmodified, tetraoctylammonium bromide-surfactant-stabilized gold nanoparticles. In between adsorbed calixarene ligands, there is accessible gold surface area in these nanoparticles, and this is measured quantitatively for the first time for a calixarene-modified nanoparticle, using a newly developed fluorescence methodology involving 2-naphthalenethiol as a relevant chemisorption probe molecule. Ligand steric bulk critically influences amount of accessible surface on the metal nanoparticle since the use of a smaller calix[4]arene ligand (MBC) results in a 7-fold lower accessible surface area relative to using 1 under otherwise similar conditions. In addition, surface coverage of 1 controls accessible surface area in an unintuitive fashion: a 4-fold increase in accessible metal surface area is observed upon increasing the surface coverage of 1 to be 1.5-fold higher than the minimum required for surface saturation. This is presumably the result of a more open ligand packing of 1 at higher surface coverages, which allows greater accessibility to 2-napthalenethiol.

Assembling gold and platinum nanoparticles on resorcinarene modified graphene and their electrochemical applications

“…[23][24][25][26][27] With marked progress, calixarenes have received special attention owing to successfully preparing calixareneencapsulated nanoparticles. [28][29][30][31][32][33][34] However, due to the poor water-solubility of calixarene, most of the calixarene-encapsulated nanoparticles are prepared, separated or applied in organic solvents such as THF, toluene, chloroform, dichloromethane, etc., [31][32][33][34] which may bring environmental pollution. Besides, it is very hard to separate or recycle calixarene-encapsulated nanoparticles from their solvents because calixareneencapsulated nanoparticles lack suitable support in the solvent, which severely limits their potential applications in the future.…”

Triosmium Clusters on a Support: Determination of Structure by X‐ray Absorption Spectroscopy and High‐Resolution Microscopy

“…Stabilized nanoparticles [1] exemplified by oxide-supported metal clusters, [2,3] have generated wide interest because they offer new and unique structures, reactivities, and catalytic properties that originate from their small sizes and interactions with the support; clusters with as few as three metal atoms have been reported. [4][5][6][7] Supported metal clusters and particles are important catalysts; the metals are typically Group 8 metals, and the supports are typically porous oxides or carbon.…”

Nature-inspired optimization of hierarchical porous media for catalytic and separation processes

“…One example of this work has been illustrated by Katz and co-workers using calixarenebound gold clusters. [42][43][44][45] In these clusters, calixarenes are bound through functional groups such as phosphines on the lower rim to the surface of the gold clusters. Synthetically, a calixarene Results are shown for a characteristic hydrolysis reaction catalyzed by lysozyme (A) and an oxidation reaction catalyzed by myoglobin (B).…”

“…This creates areas of accessible surface to which substrates can bind. [42][43][44][45] The number of accessible surface sites can be quantified with a titration procedure using strongly binding 2-napthalenethiol to count the number of sites. A correlation can be found linking gold cluster size and accessibility, as shown in Fig.…”